I had this problem some years ago. Eventually I just told everyone I would be uninstalling whatsapp on date XX/YY, which I then did. Some people installed signal and stayed in touch, others didn't. Life didn't change much.
Now I'd like to move to my own matrix server but I think appx 0.0% of my social group would follow me down that rabbit hole. :-(
More extreme, a friend of mine one day eliminated his cellphone entirely but kept Skype on his laptop. So now it's email or nothing with him and sadly it's been nothing for some time now.